1. Field of the Invention
The present invention relates to an image sensing apparatus for sensing an object image.
2. Related Background Art
Digitalization has advanced in various medical fields. A two-dimensional image sensing apparatus has been developed for digitization of images in the field of the X-ray diagnosis as well. A large image sensing apparatus with a maximum length of 43 cm has been manufactured for sensing breasts and chests.
One conventional art will be described.
A large X-ray image sensing apparatus is realized by tessellating four sensor panels, which use amorphous silicon semiconductors on a glass substrate whose size can easily be enlarged. A technology for enlarging a size of an amorphous silicon semiconductor apparatus (technology for forming a large substrate and an element thereon, or the like) which has already been established in the field of LCDs is used. As an example of this type of technology, there is one described in U.S. Pat. No. 5,315,101. A large area active array matrix described in the patent is shown in FIG. 1. Referring to FIG. 1, reference numeral 1901 denotes substrates, 1902 denotes pixels, 1903 denotes connection lead and 1904 denotes common terminals.
Another conventional art will be described next.
There is a technology for manufacturing a large X-ray image sensing apparatus using a plurality of monocrystal image sensing element (silicon or the like). As an example of this type of technology, there are ones described in U.S. Pat. Nos. 4,323,925 and 6,005,911. As a monocrystal image sensing element, there are a CCD image sensing element, an MOS type or a CMOS type image sensing element or the like. A single image sensing element has a sufficient capability to handle an X-ray motion image.
An image sensor described in U.S. Pat. No. 4,323,925 is shown in FIG. 2. Referring to FIG. 2, reference numeral 2001 denotes an object, 2002 denotes a lens, 2003 denotes an image of the subject, 2004 denotes a surface, 2005 denotes continuous optical sub-images, 2006 denotes taper-shaped FOPs (fiber optic plates), 2007 denotes image input surfaces, 2008 denotes image senor modules, 2009 denotes non-image forming peripheral areas and 2010 denotes leads. Since the optical sub-images 2005 are reduced in size by the taper-shaped FOP 2006 to be incident on the image input surfaces 2007, the non-image sensing peripheral areas 2009 are provided, to which the leads are connected.
However, the former conventional art has the following problems.
In order to form one image, only 4 pieces (2×2) sensor panels can be used at the most. This is because the image sensor has a configuration in which external terminals are provided in the external circumference of the sensor panels and a circuit for driving the sensor panels are externally connected thereto.
In addition, a size of a signal processing circuit that can be mounted on an image sensing element is limited to a such degree that the element can only have a pixel selection switch at the most. The signal processing circuit (a driver, an amplifier or the like) is externally attached.
Moreover, since an amorphous silicon does not have a good semiconductor property with respect to a high-speed operation, it is difficult to manufacture a large image forming apparatus for handling moving images. In addition, since an amorphous silicon image forming element has lower sensitivity compared with a monocrystal silicon image forming element, it is difficult to make it able to handle X-ray moving images that require high sensitivity.
In addition, the latter conventional art has the following problems.
Since the size of individual image forming element is small (in the present technology, the size of 8 inches is the largest for a wafer), 2×2 or more pieces of sensor panels are required.
In addition, a dead space is always formed in a part for joining each image sensing element in a configuration of a simple large image sensing apparatus that uses multiple monocrystal image sensing elements (areas for providing peripheral circuits such as a shift register and an amplifier, external terminals for exchanging signals and power with the outside and a protective circuit are always necessary in addition to pixel areas). This part of the dead space becomes a line defect, which lowers the image quality. Thus, light from a scintillator is guided to the image sensing elements while avoiding the dead space using taper-shaped FOPs (fiber optic plates). However, this requires extra FOPs and increases manufacturing costs. In particular, the taper-shaped FOPs are very costly.
Moreover, in the taper-shaped FOPs, the light from the scintillator tends not to be incident on the FOPs depending on a taper angle, which causes the decrease of an output light amount to offset sensitivity of the image sensing elements and lower the overall sensitivity of the apparatus.